A color reproducing device such as a scanner, a monitor, a printer, and a projector is different in a color reproduction characteristic due to difference in whether self-luminous or reflective, difference in tone representation, difference in primary colors to be used, and the like, and thus, even if the same RGB values, CMY values, or CMYK values are used, reproduced colors are largely different from one another. Therefore, to reproduce the same color on different color reproducing devices, it is necessary to represent a color in a device-independent space where a color is represented independently of characteristics of the devices, and to carry out so-called color management which determines actual ink quantities or monitor RGB values so that the colors are the same in the space.
For example, as for a color printer, on the assumption that the RGB values of a scanner, a printer, a monitor, and the like are sRGB values, which is an international standard, Lab values are calculated according to the standard from the RGB values, and then, the Lab values are color-converted to a combination of inks for reproducing a color closest to the Lab values among the colors reproducible by the printer. In general, this conversion is carried out at a predetermined grid interval in the RGB space, thereby producing a color conversion table (LUT), which carries out color conversion from RGB values to ink quantities in advance, and the color conversion table is installed in a printer driver or the like to reproduce desired colors.
Generally, a color reproduction characteristic of a printer is determined by a characteristic of what combination of inks is used (referred to as “separation” hereinafter) for input RGB values. This separation is designed to satisfy various conditions, and thus, often causes discontinuous changes in the ink quantities. Therefore, there are always areas where the ink quantities discontinuously change on a color conversion table created by simply using this separation characteristic, resulting in tone jumps. If there exists the discontinuity in the lattice, a large error occurs in linear interpolation carried out for obtaining data between the lattice points, thereby also causing a twist in the color in this case.
The present invention is devised to solve the above problems, and has a first object of providing a method of producing a color conversion table capable of restraining the color twists and the tone jumps in the output image as much as possible by correcting the discontinuities in the separation characteristic, and thus, enhancing the continuity of the color conversion table, and providing an image processing device, a method, a program, and a recording medium which use the color conversion table.
If simple smoothing is applied to the table to solve the discontinuities in the lattice, the chroma may decrease across the entire table.
Further, the present invention is devised also to solve the above problem, and has a second object of providing a method of producing a color conversion table capable of restraining the color twists and the tone jumps as much as possible while maintaining the chroma, and providing an image processing device, an image processing method, a program, and a recording medium which use the color conversion table.
Further, the present invention is devised to solve the above problem, and has a third object of providing a device, a method, and a program for producing a profile enabling color management among different color reproducing devices while restraining the color twists and the tone jumps of the output image as much as possible, and providing a recording medium for recording the program.